Stable water mist fire extinguisher is classified and belongs to the group of active fire protection that greatly increases the fire safety of buildingsThe diploma thesis deals with the topic of extinguishment using a stable extinguishing device - water mist. The work is divided into two parts.The first part contains a theoretical overview of the issue where the water mist is presented, as well as its properties affecting the function and use, types of mist devices, types of systems, their individual components, ways of dealing with the fire and its use in practice.The aim of the second part of the thesis is to design a water mist system for the object in question in a way which meets the requirements determined by the legislation. The design methodology is carried out in accordance with the relevant standards and regulation that apply to the operation, design and installation of extinguishment systems using water mist. The content consists of selecting a suitable type of water mist, placing a building in a hazard class, designing water supply, designing and distributing pipelines, selecting and placing automatic heads.By designing water mist in the object of question, we will increase the fire protection and reduce the fire hazard. It follows from this conclusion that the water mist is able to provide protection for the object.